The present embodiment relates generally to compositions and methods of utilizing the compositions for sealing a subterranean zone penetrated by a well bore and restoring lost circulation.
While drilling oil and gas wells, a drilling fluid is circulated through a drill bit in a well bore and then back to the earth surface, thereby removing cuttings from the well bore. The drilling fluid is then reconditioned and reused. In the well bore, the drilling fluid maintains a predetermined hydrostatic pressure. However, such pressure is compromised (“lost circulation”) once the drill bit encounters certain unfavorable subterranean zones, requiring remedial steps. For example, the pressure is lost when the drill bit encounters comparatively low pressure subterranean zones, such as vugs, fractures, and other thief zones. Similarly, encountering comparatively high pressure subterranean zones results in crossflows or underground blow-outs.
Most remedial steps comprise introducing a composition into the well bore to seal the above-described low pressure and high pressure subterranean zones. A cement composition can be used, but its relatively slow setting time is normally unacceptable. Much faster setting, and therefore more useful, compositions exist, for example, mixtures of clay and aqueous rubber latex or hydratable polymer (e.g., U.S. Pat. Nos. 5,913,364; 6,060,434; 6,167,967; 6,258,757) available from Halliburton Energy Services of Duncan, Okla., under the trademark “FLEXPLUG®” comprising compositions which become semi-solid upon contact with the drilling fluid, sealing the low pressure or high pressure subterranean zone. Cement can be added to the FLEXPLUG® systems where additional strength is required. However, under some circumstances, such as when re-drilling is desired, cement is undesirable, and a composition with greater flexibility and integrity is required to prevent erosion.